Shunt resistors have two terminals, which are designated hereinafter as main terminals, by means of which a resistance element is connected in series with a current to be measured. By determining the voltage dropped across the resistance element, in conjunction with the known resistance value of the resistance element, it is possible to determine the load current flowing between the main terminals. In order to obtain a highest possible measurement accuracy in this case, in principle a highest possible measurement voltage is desirable, which requires a high resistance value. On the other hand, however, the resistance value is intended to be kept as low as possible, since the power loss rises proportionally to the resistance of the resistance element. Apart from the fact that high power losses are inherently undesirable if only owing to the evolution of heat associated therewith, such evolution of heat also alters the current-voltage characteristic curve of the resistance element. Consequently, in practice, it is always necessary to find a middle course between a power loss that is just still permissible and the required measurement accuracy. However, it is not always possible to find a compromise in which all competing boundary conditions are satisfactorily fulfilled.
This is aggravated by the fact that the currents to be measured in a circuit arrangement with a shunt resistor, for example if the currents flow in the conductor plane of a printed circuit board, can vary with regard to their current distribution over the conductor plane in a manner dependent on the respective circuit state, such that the result of a current measurement is greatly dependent on the current distribution in the respective circuit state of the circuit arrangement. Thus, in the case of circuit arrangements in power semiconductor modules comprising a bridge circuit, current-direction-dependent deviations of the measured current value from the actual current value of up to 2% have been determined. However, it would be desirable to achieve deviations of 1% or less.
In the manufacture of a plurality of identical circuit arrangements having, in particular, assemblies for current measurement with a shunt resistor, measurement inaccuracies can likewise occur. In the ideal case, the taps by which the voltage dropped across the shunt resistor is tapped off are fitted exactly at correspondingly identical locations in the different circuit arrangements. In practice, however, deviations from the ideal case arise on account of unavoidable manufacturing tolerances, such that, in the different circuit arrangements with analogously identical potential tapping in each case, with otherwise identical construction and identical energization conditions of the different circuit arrangements, different potentials are tapped off.
Furthermore, conventional shunt resistors typically have two main terminals, which are both soldered via the metallization of a circuit carrier. Such a construction requires a large amount of space on the circuit carrier, which is manifested in the costs. This is relevant primarily when an expensive ceramic substrate is used as the circuit carrier. Moreover, mounting such a shunt resistor on the circuit carrier requires a dedicated process technology, which likewise increases the manufacturing outlay and the production costs. Moreover, shunt resistors require a longer energization path on account of their design, as a result of which the inductance is significantly increased. As a result, however, particularly in fast switching operations, high induced voltages can occur, which can corrupt the measurement signal tapped off at the shunt resistor.